The lines begin to blur
The New York Times has look at the Met's HD broadcasts, which includes an interesting take on the performance differences. Movies are very different from plays and operas. The director controls what you see, and the closeups make you relate differently to the actors than you do at the remove provided by the stage. At a play you're always aware you're watching something artificial - it's not worse, it's not better, but it is different.
I was thinking a bit of this last night at the Hippodrome, with every performer miked. Stage actors have to play to the last row in the balcony - I hope they don't forget that when they no longer have to project!